diff options
Diffstat (limited to 'pkg/sentry/fsimpl/kernfs')
| -rw-r--r-- | pkg/sentry/fsimpl/kernfs/BUILD | 26 | ||||
| -rw-r--r-- | pkg/sentry/fsimpl/kernfs/kernfs.go | 196 |
2 files changed, 182 insertions, 40 deletions
diff --git a/pkg/sentry/fsimpl/kernfs/BUILD b/pkg/sentry/fsimpl/kernfs/BUILD index 4de1e6922..aaad67ab8 100644 --- a/pkg/sentry/fsimpl/kernfs/BUILD +++ b/pkg/sentry/fsimpl/kernfs/BUILD @@ -4,6 +4,18 @@ load("//tools/go_generics:defs.bzl", "go_template_instance") licenses(["notice"]) go_template_instance( + name = "dentry_list", + out = "dentry_list.go", + package = "kernfs", + prefix = "dentry", + template = "//pkg/ilist:generic_list", + types = { + "Element": "*Dentry", + "Linker": "*Dentry", + }, +) + +go_template_instance( name = "fstree", out = "fstree.go", package = "kernfs", @@ -27,17 +39,6 @@ go_template_instance( ) go_template_instance( - name = "dentry_refs", - out = "dentry_refs.go", - package = "kernfs", - prefix = "Dentry", - template = "//pkg/refsvfs2:refs_template", - types = { - "T": "Dentry", - }, -) - -go_template_instance( name = "static_directory_refs", out = "static_directory_refs.go", package = "kernfs", @@ -84,7 +85,7 @@ go_template_instance( go_library( name = "kernfs", srcs = [ - "dentry_refs.go", + "dentry_list.go", "dynamic_bytes_file.go", "fd_impl_util.go", "filesystem.go", @@ -105,6 +106,7 @@ go_library( "//pkg/log", "//pkg/refs", "//pkg/refsvfs2", + "//pkg/sentry/fs/fsutil", "//pkg/sentry/fs/lock", "//pkg/sentry/kernel/auth", "//pkg/sentry/kernel/time", diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go index 25184dbf9..5c5e09ac5 100644 --- a/pkg/sentry/fsimpl/kernfs/kernfs.go +++ b/pkg/sentry/fsimpl/kernfs/kernfs.go @@ -107,6 +107,17 @@ type Filesystem struct { // nextInoMinusOne is used to to allocate inode numbers on this // filesystem. Must be accessed by atomic operations. nextInoMinusOne uint64 + + // cachedDentries contains all dentries with 0 references. (Due to race + // conditions, it may also contain dentries with non-zero references.) + // cachedDentriesLen is the number of dentries in cachedDentries. These + // fields are protected by mu. + cachedDentries dentryList + cachedDentriesLen uint64 + + // MaxCachedDentries is the maximum size of cachedDentries. If not set, + // defaults to 0 and kernfs does not cache any dentries. This is immutable. + MaxCachedDentries uint64 } // deferDecRef defers dropping a dentry ref until the next call to @@ -165,7 +176,12 @@ const ( // +stateify savable type Dentry struct { vfsd vfs.Dentry - DentryRefs + + // refs is the reference count. When refs reaches 0, the dentry may be + // added to the cache or destroyed. If refs == -1, the dentry has already + // been destroyed. refs are allowed to go to 0 and increase again. refs is + // accessed using atomic memory operations. + refs int64 // fs is the owning filesystem. fs is immutable. fs *Filesystem @@ -177,6 +193,12 @@ type Dentry struct { parent *Dentry name string + // If cached is true, dentryEntry links dentry into + // Filesystem.cachedDentries. cached and dentryEntry are protected by + // Filesystem.mu. + cached bool + dentryEntry + // dirMu protects children and the names of child Dentries. // // Note that holding fs.mu for writing is not sufficient; @@ -188,6 +210,150 @@ type Dentry struct { inode Inode } +// IncRef implements vfs.DentryImpl.IncRef. +func (d *Dentry) IncRef() { + // d.refs may be 0 if d.fs.mu is locked, which serializes against + // d.cacheLocked(). + atomic.AddInt64(&d.refs, 1) +} + +// TryIncRef implements vfs.DentryImpl.TryIncRef. +func (d *Dentry) TryIncRef() bool { + for { + refs := atomic.LoadInt64(&d.refs) + if refs <= 0 { + return false + } + if atomic.CompareAndSwapInt64(&d.refs, refs, refs+1) { + return true + } + } +} + +// DecRef implements vfs.DentryImpl.DecRef. +func (d *Dentry) DecRef(ctx context.Context) { + if refs := atomic.AddInt64(&d.refs, -1); refs == 0 { + d.fs.mu.Lock() + d.cacheLocked(ctx) + d.fs.mu.Unlock() + } else if refs < 0 { + panic("kernfs.Dentry.DecRef() called without holding a reference") + } +} + +// cacheLocked should be called after d's reference count becomes 0. The ref +// count check may happen before acquiring d.fs.mu so there might be a race +// condition where the ref count is increased again by the time the caller +// acquires d.fs.mu. This race is handled. +// Only reachable dentries are added to the cache. However, a dentry might +// become unreachable *while* it is in the cache due to invalidation. +// +// Preconditions: d.fs.mu must be locked for writing. +func (d *Dentry) cacheLocked(ctx context.Context) { + // Dentries with a non-zero reference count must be retained. (The only way + // to obtain a reference on a dentry with zero references is via path + // resolution, which requires d.fs.mu, so if d.refs is zero then it will + // remain zero while we hold d.fs.mu for writing.) + refs := atomic.LoadInt64(&d.refs) + if refs == -1 { + // Dentry has already been destroyed. + panic(fmt.Sprintf("cacheLocked called on a dentry which has already been destroyed: %v", d)) + } + if refs > 0 { + if d.cached { + d.fs.cachedDentries.Remove(d) + d.fs.cachedDentriesLen-- + d.cached = false + } + return + } + // If the dentry is deleted and invalidated or has no parent, then it is no + // longer reachable by path resolution and should be dropped immediately + // because it has zero references. + // Note that a dentry may not always have a parent; for example magic links + // as described in Inode.Getlink. + if isDead := d.VFSDentry().IsDead(); isDead || d.parent == nil { + if !isDead { + d.fs.vfsfs.VirtualFilesystem().InvalidateDentry(ctx, d.VFSDentry()) + } + if d.cached { + d.fs.cachedDentries.Remove(d) + d.fs.cachedDentriesLen-- + d.cached = false + } + d.destroyLocked(ctx) + return + } + // If d is already cached, just move it to the front of the LRU. + if d.cached { + d.fs.cachedDentries.Remove(d) + d.fs.cachedDentries.PushFront(d) + return + } + // Cache the dentry, then evict the least recently used cached dentry if + // the cache becomes over-full. + d.fs.cachedDentries.PushFront(d) + d.fs.cachedDentriesLen++ + d.cached = true + if d.fs.cachedDentriesLen <= d.fs.MaxCachedDentries { + return + } + // Evict the least recently used dentry because cache size is greater than + // max cache size (configured on mount). + victim := d.fs.cachedDentries.Back() + d.fs.cachedDentries.Remove(victim) + d.fs.cachedDentriesLen-- + victim.cached = false + // victim.refs may have become non-zero from an earlier path resolution + // after it was inserted into fs.cachedDentries. + if atomic.LoadInt64(&victim.refs) == 0 { + if !victim.vfsd.IsDead() { + victim.parent.dirMu.Lock() + // Note that victim can't be a mount point (in any mount + // namespace), since VFS holds references on mount points. + d.fs.vfsfs.VirtualFilesystem().InvalidateDentry(ctx, victim.VFSDentry()) + delete(victim.parent.children, victim.name) + victim.parent.dirMu.Unlock() + } + victim.destroyLocked(ctx) + } + // Whether or not victim was destroyed, we brought fs.cachedDentriesLen + // back down to fs.MaxCachedDentries, so we don't loop. +} + +// destroyLocked destroys the dentry. +// +// Preconditions: +// * d.fs.mu must be locked for writing. +// * d.refs == 0. +// * d should have been removed from d.parent.children, i.e. d is not reachable +// by path traversal. +// * d.vfsd.IsDead() is true. +func (d *Dentry) destroyLocked(ctx context.Context) { + switch atomic.LoadInt64(&d.refs) { + case 0: + // Mark the dentry destroyed. + atomic.StoreInt64(&d.refs, -1) + case -1: + panic("dentry.destroyLocked() called on already destroyed dentry") + default: + panic("dentry.destroyLocked() called with references on the dentry") + } + + d.inode.DecRef(ctx) // IncRef from Init. + d.inode = nil + + // Drop the reference held by d on its parent without recursively locking + // d.fs.mu. + if d.parent != nil { + if refs := atomic.AddInt64(&d.parent.refs, -1); refs == 0 { + d.parent.cacheLocked(ctx) + } else if refs < 0 { + panic("kernfs.Dentry.DecRef() called without holding a reference") + } + } +} + // Init initializes this dentry. // // Precondition: Caller must hold a reference on inode. @@ -197,6 +363,7 @@ func (d *Dentry) Init(fs *Filesystem, inode Inode) { d.vfsd.Init(d) d.fs = fs d.inode = inode + atomic.StoreInt64(&d.refs, 1) ftype := inode.Mode().FileType() if ftype == linux.ModeDirectory { d.flags |= dflagsIsDir @@ -204,7 +371,6 @@ func (d *Dentry) Init(fs *Filesystem, inode Inode) { if ftype == linux.ModeSymlink { d.flags |= dflagsIsSymlink } - d.EnableLeakCheck() } // VFSDentry returns the generic vfs dentry for this kernfs dentry. @@ -222,32 +388,6 @@ func (d *Dentry) isSymlink() bool { return atomic.LoadUint32(&d.flags)&dflagsIsSymlink != 0 } -// DecRef implements vfs.DentryImpl.DecRef. -func (d *Dentry) DecRef(ctx context.Context) { - decRefParent := false - d.fs.mu.Lock() - d.DentryRefs.DecRef(func() { - d.inode.DecRef(ctx) // IncRef from Init. - d.inode = nil - if d.parent != nil { - // We will DecRef d.parent once all locks are dropped. - decRefParent = true - d.parent.dirMu.Lock() - // Remove d from parent.children. It might already have been - // removed due to invalidation. - if _, ok := d.parent.children[d.name]; ok { - delete(d.parent.children, d.name) - d.fs.VFSFilesystem().VirtualFilesystem().InvalidateDentry(ctx, d.VFSDentry()) - } - d.parent.dirMu.Unlock() - } - }) - d.fs.mu.Unlock() - if decRefParent { - d.parent.DecRef(ctx) // IncRef from Dentry.insertChild. - } -} - // InotifyWithParent implements vfs.DentryImpl.InotifyWithParent. // // Although Linux technically supports inotify on pseudo filesystems (inotify |